Sealing ejector pin

ABSTRACT

The invention relates to an ejector pin receivable in a mold part of a mold for encapsulating electronic components mounted on a carrier, wherein the substantially cylindrical ejector pin is provided with a side wall in which at least one recess is arranged close to the end which makes contact with the product for ejecting. The invention also relates to a mold part in which an opening is arranged for guiding an ejector pin, wherein at least one recess is arranged in the wall of the opening. The invention further includes a mold for encapsulating electronic components, in addition to a method for sealing an interspace between an ejector pin and an opening in a mold part.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an ejector pin receivable in a mould part of amould for encapsulating electronic components mounted on a carrier. Theinvention also includes a mould part of a mould and a mould forencapsulating electronic components mounted on a carrier and a methodfor sealing an interspace formed by an ejector pin received in anopening in a mould part of a mould for encapsulating electroniccomponents mounted on a carrier.

2. Description of the Prior Art

When encapsulating electronic components, such as for instance leadframes, mounted on a carrier, it is important that the encapsulatingmaterial completely fills a mould cavity during the encapsulatingprocess. It is also important that the encapsulating material adheresfirmly to the carrier after the encapsulating process, this to preventrelease of the encapsulating material from the carrier. After anencapsulating process the encapsulated product must be removed from anopened mould. In order to facilitate the release and subsequent removalof the encapsulated product from the mould, existing moulds are usuallyprovided with ejector pins. The drawback of using ejector pins in amould is that encapsulating material can enter the space between anejector pin and a mould part, whereby the relevant ejector pin becomesjammed in the mould or is less easily movable. This problem becomes evenmore relevant in the encapsulation of electronic components mounted onso-called BGAs (Ball Grid Arrays), wherein the moulding can only adhereto one side of the carrier. The encapsulating materials developed forthis purpose adhere more strongly to the carrier than the encapsulatingmaterials used with the conventional lead frames but therein alsoincrease the danger of one or more ejector pins jamming in a mould.

SUMMARY OF THE INVENTION

The present invention has for its object to provide an improved ejectorpin, mould part and mould, in addition to a method with which the chanceof an ejector pin jamming in a mould can be considerably reduced.

To this end the invention provides an ejector pin receivable in a mouldpart of a mould for encapsulating electronic components mounted on acarrier, wherein the substantially cylindrical ejector pin is providedwith a side wall in which at least one recess is arranged close to theend which makes contact with the product for ejecting.

The recess is preferably at least one annular groove running round theejector pin. It is also possible herein that the recess comprises atleast one channel running from the annular groove to the end of theejector pin making contact with a product for ejecting. Due to therecess in the ejector pin the encapsulating material which penetratesbetween the ejector pin and the opening in which the ejector pin isguided will flow at least partially into the recess. After a fewencapsulating processes the recess will therefore be completely filledwith encapsulating material, which encapsulating material will also cureafter a time. This cured encapsulating material is rigidly connected tothe ejector pin since it adheres onto the recess in the ejector pin. Theencapsulating material thus rigidly connected to the ejector pin thereinfunctions as seal, so that no more encapsulating material can penetrateinto the interspace. In the case of wear of the encapsulating materialor the opening into which the ejector pin is guided new encapsulatingmaterial will be supplied which will subsequently adhere to theencapsulating material already rigidly connected to the ejector pin.After a time this new encapsulating material will cure so that the sealis again adapted to the changed conditions. This manner of sealing theinterspace requires few constructive measures and, very importantly,requires practically no maintenance during encapsulation of productssince the seal is self-regulating. The shape of the recess in theejector pin depends on the dimensions of the ejector pin and guideopening and also depends on the encapsulating material in use.Particularly favourable results are obtained with an annular recess,also because incomplete sealing of the interspace can hereby berealized. For the purpose of filling the recess in the ejector pin in ashort time, channels can be arranged with which encapsulating materialis carried to the recess.

The present invention also relates to a mould part of a mould forencapsulating electronic components mounted on a carrier, which mouldpart is provided with at least one substantially cylindrical opening forguiding an ejector pin, wherein at least one recess is arranged in thewall of the opening. The recess is herein at least one annular grooverunning round the wall of the opening. It is also possible that the wallof the opening comprises at least one channel which connects the annulargroove to a surface of the mould part at least partially co-defining amould cavity. Using such a mould part it is possible to realize a sealin the interspace formed by ejector pin and opening in the mould part bymeans of encapsulating material which enters the interspace and flowsinto the recess in the opening of the mould part. Analogous to thediscussion of the above described ejector pin, the encapsulatingmaterial will cure in the interspace, wherein it is however not rigidlyconnected to the ejector pin but to the mould part. When the ejector pinmoves, the seal formed by cured encapsulating material will nottherefore co-displace when the recess is situated in the opening of amould part. In the case of the mould part favourable results are alsoobtained with a recess consisting of at least one annular groove runninground the wall of the opening. For a rapid filling of the annular grooveat least one channel can herein also be provided which connects theannular groove to the mould cavity into which the encapsulating materialis introduced.

The invention also includes a mould in which is situated at least oneejector pin and/or mould part according to the invention. It is notedherein that it is also possible to realize a double seal, wherein arecess is arranged in the opening as well as in the ejector pin. In sucha construction at least two seals formed by curing encapsulatingmaterial will be created, wherein one is rigidly connected to theopening and one is rigidly connected to the ejector pin. In the placingof the recesses the stroke length through which the ejector pin travelsmust then be taken into account, since the two cured encapsulatingmaterial portions may not obstruct each other during the stroke.

Finally, the invention also includes a method for sealing an interspaceformed by an ejector pin received in an opening in a mould part of amould for encapsulating electronic components mounted on a carrier,comprising the steps of:

introducing viscous encapsulating material into a mould cavity at leastpartially co-defined by the mould part;

admitting a portion of the encapsulating material between the ejectorpin and the mould part such that a recess in the ejector pin and/or arecess in the opening in the mould part is filled therewith; and

causing the encapsulating material to cure in the recess so that thecured encapsulating material forms a seal.

Using this method, a seal can be realized in the interspace in verysimple manner, as already elucidated in the foregoing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-section through a schematically representedencapsulating device for encapsulating electronic components;

FIG. 2 shows a cross-section through a mould according to the inventionduring the encapsulating process;

FIG. 3 shows a cross-section through a mould as shown in FIG. 2 afterthe encapsulating process;

FIG. 4 shows a cross-section through a part of an ejector pin accordingto the invention; and

FIG. 5 shows a cross-section through an opening in a mould partaccording to the invention, in which opening is situated an ejector pin.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows an encapsulating device 1 in which two mould halves 2,3 arearranged. Mould halves 2,3 enclose two mould cavities 4,5 into whichencapsulating material 7 is introduced by means of a plunger 6. Situatedin mould halves 2,3 are ejector pins 8 with which an encapsulatedproduct can be pushed out of mould cavities 4,5 after the encapsulatingprocess.

FIG. 2 shows in more detail a part of the mould halves 2,3 between whicha lead frame 9 is clamped. Mounted on lead frame 9 is an electroniccomponent 10, for instance a chip. In FIG. 2, encapsulating material 7is applied on two sides of lead frame 9. It is however also possible toapply on only one side of a lead frame 9 (for instance a BGA), in whichcase the present invention is particularly advantageous. Ejector pins 8are displaceable in the mould halves 2,3. During the encapsulatingprocess the ejector pins 8 are withdrawn almost completely from mouldcavity 5. Close to mould cavity 5 the ejector pins 8 are provided with arecess, preferably an annular groove 11 which encapsulating material 7can enter and after curing functions as seal.

FIG. 3 shows the part of the encapsulating device 1 shown in FIG. 2after the encapsulating process is completed and encapsulating material7 has cured. Mould halves 2,3 are moved apart and ejector pins 8 aremoved as according to arrows P1, P2 relative to the respective mouldhalves 2,3. During displacement of ejector pins 8 relative to mould half2,3 the encapsulated product 12 is released from the mould cavity walls5. FIG. 2 also shows that ejector-pins 8 are provided with sealing edges13 consisting of encapsulating material 7 which has cured in the annulargrooves 11 of ejector pin 8.

FIG. 4 shows in detail a view of the active end of an ejector pin 8 inwhich an annular groove 11 is arranged which has not yet been filledwith encapsulating material 7, i.e. the ejector pin 8 as shown in thisfigure has not yet been used in an encapsulating process. In mould half3 is arranged an opening 14 through which the ejector pin 8 is guidedand an annular groove 19 which encapsulating material can enter. Presentbetween opening 14 and ejector pin 8 are interspaces 15 in the form ofgaps whereby a limited quantity of encapsulating material can penetratebetween the ejector pin 8 and the wall of the opening 14. The presenceof interspaces 15 can never be wholly prevented due to the fact thatejector pin 8 must be axially movable in the opening 14 of mould half 3.

FIG. 5 shows a mould half 16 in which is arranged an opening 17, theupper part of which connects close-fittingly on an ejector pin 18. Theupper part of opening 17 therefore forms the part which guides theejector pin 18. In the wall of opening 17 is arranged a recesspreferably an annular groove 19 which encapsulating material 7 canenter. Since annular groove 19 in FIG. 5 is not yet filled withencapsulating material, this means that mould half 16 has not yet beenused for encapsulating products, as the annular groove 19 would then befilled with encapsulating material 7.

What is claimed is:
 1. A mould part of a mould for encapsulatingelectronic components mounted on a carrier comprising: a mould parthaving a wall forming at least one cylindrical opening for guiding anejector pin and at least one recess arranged in the wall of the opening;a cylindrical ejector pin having a side wall and at least one ejectorpin recess arranged close to an end of the ejector pin which makescontact with a product for ejecting; and a self-regulating seal formedin the recess arranged in the wall of the opening by encapsulatingmaterial which has been received therein, wherein the ejector pin movesrelative to the self-regulating seal.
 2. The mould part of a mould forencapsulating electronic components mounted on a carrier as claimed inclaim 1, wherein the ejector pin recess is an annular groove arrangedadjacent the end of the ejector pin.
 3. The mould part of a mould forencapsulating electronic components mounted on a carrier as claimed inclaim 2, wherein the ejector pin recess is the annular groove and aninterspace running from the annular groove to the end of the ejector pinmaking contact with a product for ejecting.
 4. The mould part of a mouldfor encapsulating electronic components mounted on a carrier as claimedin claim 1, wherein the wall of the opening forms at least one channelwhich connects the annular groove to the surface of the mould part atleast partially co-defining a mould cavity.
 5. The mould part of a mouldfor encapsulating electronic components mounted on a carrier as claimedin claim 1 wherein the ejector pin recess is configured to receiveencapsulating material so as to form a seal.